Renewable Energy Process and Method Using a Carbon Dioxide Cycle to Produce Work

ABSTRACT

A renewable energy process and method to capture heat from low temperature sources with a refrigeration cycle to produce electricity using the heat content of sources normally unavailable because of their low temperature. This disclosure uses carbon dioxide (CO 2 ) refrigerate, but other refrigerates may be used as well. Heat is transferred from a low temperature source through an indirect heat exchanger (evaporator) to a refrigerating agent that enters the evaporator as a low temperature sub-cooled liquid or saturated mixture and exits as a vapor. The vapor is then superheated by a pollution free method and directed to a turbine for expansion to produce work. The expanded vapor is converted back to liquid without a condenser for return to the evaporator, resulting in a highly efficient system that does not reject heat into the environment.

RELATED APPLICATION

This application claims priority as a continuation-in-part of U.S.Provisional Patent Application No. 62/627,251 entitled “Renewable EnergyProcess and Method Using Carbon Dioxide Cycle to Produce Work”, filedFeb. 7, 2018.

BACKGROUND OF THE INVENTION 1. Field of the Invention

Specifically, the present invention is a process for a refrigerationcycle to produce work from heat sources, heretofore not commerciallyavailable because of their low temperatures. Heat may be extracted fromany available low temperature source, including solar heated ponds,solar mirror focused heat, geothermal sources, power plant condenser andstack rejected heat, waste heat, solids, molten salt, or vacuum typedesalination plants as referenced herein.

Heat is transferred from a low temperature source to the cycle throughan indirect heat exchanger (evaporator) to a refrigerating agent thatenters the evaporator as a low temperature sub-cooled liquid orsaturated mixture and exits as a vapor. This disclosure uses carbondioxide (CO₂) refrigerate, but other refrigerates may be used as well.The vapor is then superheated by a pollution free method to produce workand then regenerated to a liquid without use of a condenser forreturning to the evaporator.

This process can serve as a stand-alone plant using input from arenewable energy source and not requiring input from fossil or nuclearfuel. It may be integrated with a power plant to recover rejected heatfrom the plant's condenser and stack gas to significantly improvecombined plant thermal efficiency and increase output. A conventionalsteam power plant using the Rankine Cycle rejects approximately 55% ofits fuel heat input in the condenser and 10% from the stack, resultingin a plant thermal efficiency of 35-40%. This combined CO₂ process andconventional plant can increase plant thermal efficiency up to 70%,generating more power without additional pollutant discharges to theenvironment. This disclosed cycle may be integrated with a Brayton Cycleor other waste heat sources.

Another feature of this process includes its capability to produce bothelectrical power and desalinated water, by combining this disclosurewith a unique steam flash tower as the low temperature heat source asdisclosed in U.S. Pat. No. 9,816,400 B1 entitled “Process and MethodUsing Low Temperature Sources to Produce Electric Power and DesalinateWater”, which patent is by the inventor of this application and isincorporated herein by reference. The combined plant can generaterevenues from electricity and desalinated water products, or the plantowner may choose to market the heat content of condenser cooling waterto another party.

This invention allows power shifting from less efficient plants toretrofitted or new plants with a corresponding credit for reductions inemission of pollutants and CO₂, and without requiring the addition ofhigh cost pollution collecting equipment. This invention can eliminatecooling towers or the need to locate a plant near a large cooling watersource. Water discharge temperature violations, water intake orcondenser fouling problems, environmental bio-equilibrium impacts, andforced load reductions during peak summer demand seasons would no longerbe issues. Power plant efficiency can improve by returning the coolingwater to the condenser at a lower temperature than it received throughexisting cooling equipment, producing more power output with theresulting reduction in condenser vacuum.

2. Prior Art Description

Various prior art is available for high temperature supercriticalpressure CO₂ power cycles fueled by waste heat gas in the temperaturerange of 400° F., fossil fuels, or nuclear fuel. This disclosure uses alow temperature sub-critical pressure CO₂ power cycle fueled by lowtemperature sources at a minimum temperature of at least 60° F., and forwhich equipment is currently available and by which pollutants are notproduced.

Prior art is taught by the referenced US Patent to use a CO₂ cycle toproduce desalinated water and electricity from power plant cooling wateras a low temperature heat source. This disclosure produces electricityfrom low temperature heat sources but is unique with other equipmentselections, with the process refrigerate flow paths through theequipment, and in the method to transition vapor back to liquid withouta condenser.

Prior art has not disclosed this type of CO₂ cycle to produce work.Existing fossil fueled power plants have environmental issues and alsoissues with dissipation of rejected heat, ash disposal, and lowefficiency operation wasting up to 60% of the fuel input.

Geothermal power plants currently operate at efficiencies of up to 20%.This disclosed process can be applied to geothermal power plants toachieve efficiencies of more than 50%.

Prior art exists for high temperature solar thermal power plants. Thisdisclosure provides a method to produce low temperature solar thermalpower plants, which eliminates the need for large mirror fields toconcentrate high temperature solar heat that is harmful to flying birdsand creates more expensive plant equipment. The low temperature heatsource for this disclosure requires smaller mirror fields and alsoprovides for more effective use of solar heat storage.

Other than hydropower and geothermal, prior art has not disclosed aneconomical system to produce large amounts of renewable, cleanelectricity with a high capacity factor. This disclosure includes theseattributes, besides removing CO₂ and other pollutants from theenvironment.

SUMMARY OF THE INVENTION

This invention consists of a CO₂ cycle that uses a refrigerating agentwith inherent capabilities of vaporizing at low temperature in threeconcurrent cycles to produce work. Heat input to the evaporator can betaken from various sources, including rejected heat from a water-steamcycle, waste heat, or a renewable energy heat source. Since organicrefrigerates are costly and environmentally unfriendly, CO₂ agent is thepreferred refrigerate in this disclosure. CO₂ is safely removed from theenvironment and provides a non-toxic workplace environment.

The evaporator refrigerate operates at sub-critical pressure to which astartup pump located in the storage tank area initially supplies a CO₂sub-cooled liquid to an expansion valve which controls evaporatorpressure and the corresponding saturation temperature. Heat input to theevaporator is supplied from a low temperature heat source, which is at ahigher temperature than the refrigerate saturation temperature.

The refrigerate absorbs heat in the evaporator and exits as a saturatedor slightly superheated vapor. The CO₂ vapor is then split into threepaths (A, B, and C). Path A is directed to a first stage indirect heaterand path B is directed to a compressor. Path B is compressed to asupercritical pressure vapor and superheated by the heat of compression,and is then split into two paths (B1 and B2) when exiting thecompressor. Path B1 supplies the first stage indirect heater, whereinpath A is superheated and then directed to a turbine for isentropicexpansion to produce electricity with a shaft-connected generator beforeexhausting the turbine as a lower pressure superheated vapor. Path A isthen directed from the turbine to a second stage indirect heater forreheating by path B2. Path A is then directed to a reheat turbine forexpansion and to produce additional work. Paths B1 and B2 recombine intopath B when exiting the two stages of indirect heat exchangers, which isthen directed to a liquid turbo-expander with a generator to producepower and conserve energy.

Path A exits the final reheat turbine as a low pressure superheatedvapor and isentropically expands through a gas turbo-expander to producea cooler vapor and additional power with a shaft-connected generator.The cooler vapor is then directed to a manifold header for batchdistribution to multiple trains of duplicate deposition-transition (D-T)vessels arranged in parallel flow circuits, which are sequentiallyoperated to provide a continuous process. The D-T vessels are equippedwith inlet venturi nozzles to isentropically expand the cooler vapor forfurther cooling to a temperature of −109.3° F. to affect snow-like dryice deposition at 14.7 psia pressure. To ensure a total vapor phasechange to dry ice, nitrogen gas at a temperature of less than −150° F.is directed into the throat of the venturi nozzle so that the mixturetemperature is at least 25° F. below the CO₂ deposition temperature. Tofurther ensure deposition, the atmosphere inside the D-T vessel consistsof nitrogen gas at a temperature of less than −150° F. and a pressure sothat the CO₂ vapor partial pressure is at least 14.7 psia. The D-Tvessel jacket enclosure atmosphere also consists of nitrogen gas at atemperature of less than −150° F.

After the D-T vessel receives its full measure of dry ice and nitrogengas is vented back to the storage tank area, the D-T vessel is isolatedby valving and pressurized by a portion of path C vapor to 100 psia(above the triple point pressure) to prevent sublimation to a vapor andfacilitate transition to a sub-cooled liquid. Then, the D-T vessel isheated and pressurized to 900 psia by the remaining portion of path Cvapor; thereby, completing the transitioning of any remaining dry ice toa sub-cooled liquid. Higher pressure nitrogen gas is reintroduced to theD-T vessel to facilitate draining and replacing of the sub-cooled liquidas it is drained to a mixing manifold for merging with path B sub-cooledliquid leaving the turbo-generator.

The mixture in the mixing manifold is a regeneration of the sub-cooledprocess refrigerate at a temperature of at least 5° F. above thefreezing point temperature of water. The process refrigerate is thenreturned to the evaporator through an expansion valve; wherein thepressure is controlled so that the saturation temperature of the processrefrigerate in the evaporator is at least 5° F. below the temperature ofthe entering temperature of the low temperature heat source; thereby,completing paths A, B, and C cycles.

The jacket enclosing the D-T vessel is provided a cold nitrogen gasduring the deposition process and a warmer nitrogen gas during thetransition process as insulation against heat loss.

During operation of the D-T vessels and their jackets, vents and drainsto the storage tanks may be controlled with ejectors or vacuum pumps toenable evacuation and control of operating pressure and temperature.Vents may be heat traced to prevent dry ice blockage.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 schematically illustrates this disclosure to capture heat fromlow temperature sources to produce pollution-free work and to convertthe expanded first path vapor back to sub-cooled liquid without acondenser.

FIG. 1A schematically illustrates the disclosure for applications inwhich higher temperature heat sources are available to superheat andreheat path A; thereby, eliminating the path B circuit.

FIG. 2 is a marked CO₂ pressure-enthalpy (P-H) diagram to illustrate anapproximate example of the disclosed cycle.

FIG. 3 depicts a phase diagram showing the physical states of CO₂ underdifferent pressure and temperatures.

DETAILED DESCRIPTION

FIG. 1 schematically illustrates process 1 of this disclosure. Duringstartup, a sub-cooled liquid process refrigerate at a temperature of atleast 5° F. above the freezing point temperature of water (32° F.) isdirected from storage tank area 50 by a pump to expansion valve 34,which controls pressure to evaporator 30 and to provide a saturationtemperature of at least 5° F. below the entering temperature of the lowtemperature source 51. A heat content is transferred from lowtemperature source 51 to the process refrigerate in evaporator 30, afterwhich the process refrigerate exits evaporator 30 as a saturated orslightly superheated vapor. Remaining heat content in low temperaturesource 51 is returned to the source through 51R if applicable.

The process refrigerate vapor leaving evaporator 30 is then divided intothree separate flow paths (A, B, and C). Path A is directed to firststage indirect heater 30-1 for superheating. Path B is directed to theinlet of compressor 31 wherein it is compressed into a supercriticalpressure vapor and superheated by the heat of compression. Compressor 31is driven by electric motor M during startup and low loads and thenswitched to turbine 32-2 drive by hydraulic coupling 53 during higherloads. Path B exiting compressor 31 is split into two paths (B1 and B2).Path B1 is directed to first stage indirect heater 30-1, wherein path Ais superheated for supplying turbine 32-1 for isentropic expansion toproduce work through electric generator G1. Path A exiting turbine 32-1flows to second stage indirect heater 30-2 for reheating to a highersuperheat temperature by path B2. Path A exiting indirect heater 30-2flows to reheat turbine 32-2 for isentropic expansion and to producework through electric generator G2.

Path B1 and path B2 exit indirect heaters 30-1 and 30-2 and recombine toform path B supercritical pressure liquid for directing to liquidturbo-expander 32-3 to produce work through electric generator G3;thereby lowering path B pressure and forming a sub-cooled liquid tomerge in mixing manifold 41 with the sub-cooled liquid leaving D-Tvessel 33-1.

Path A superheated vapor leaving final reheat turbine 32-2 is convertedback to a sub-cooled liquid in D-T vessel 33-1. All D-T vessels (33-1,33-2, and 33-3) and associated equipment are duplicates as are thedeposition and transition details. Path A leaving reheat turbine 32-2 isdirected to gas turbo-expander 32-4, wherein the superheated vapor isisentropically expanded and cooled to a temperature of −80° F. at apressure of 25 psia; thereby, producing a cooler path A vapor andproducing work through electric generator G4. The cooler path A vapor isthen directed to manifold header 38 for distribution to parallel trainsof D-T vessels 33. In this disclosure, D-T vessels 33-1, 33-2 and 33-3are referred to collectively as D-T vessels 33. This portion of thecycle is a batch process with the parallel trains operated sequentiallyto provide a continuous overall process in vapor deposition to dry iceand then dry ice transition to sub-cooled liquid for cycling back toevaporator 30 as the process refrigerate.

The cooler path A vapor leaving manifold 38 is directed through aselected shut-off valve 35 to venturi nozzle 36 at the inlet to D-Tvessel 33-1, wherein path A vapor is isentropically expanded to apressure just above atmospheric pressure, resulting in a path A vaportemperature near the dry ice deposition of −109.3° F. as may bereferenced on FIGS. 3 and 4. Those skilled in the arts may reference aCO₂ T-S (Temperature-Entropy) diagram, which may better demonstrate lowpressure and temperature isentropic expansion. To ensure a total phasechange to dry ice, a much cooler nitrogen gas spray S_(N2) is introducedthrough control valve 46 to the throat of venturi nozzle 36 to cool themixture to less than −125° F. To further facilitate deposition, D-Tvessel 33-1 is controlled in a nitrogen gas atmosphere, by valve 43 inconnection V_(N2) and valve 49 in vent V₃₃, to a temperature of at least−150° F. and at a pressure so that the entering CO₂ vapor partialpressure is at least 14.7 psia. Also, D-T vessel jacket 33J is operatedin a nitrogen gas atmosphere at less than −150° F. through control valve45 in connection J_(N2) and control valve 48 in vent connection JV.After the selected D-T vessel 33-1 has achieved its full measure of dryice of snow-like consistency, shut-off valve 35 is closed and nitrogengas in D-T vessel 33-1 is vented back to storage tank area 52 throughcontrol valve 49 in vent connection V₃₃.

With D-T vessel 33-1 isolated, a portion of path C pressurizes D-Tvessel 33-1 above 100 psia through connection PC and control valve 44 toprevent sublimation of dry ice to vapor and facilitate transition to asub-cooled liquid. Then, D-T vessel 33-1 is heated and pressurized to900 psia by the remaining portion of path C vapor through connection PCand valve 44, thereby completing the transitioning of dry ice tosub-cooled liquid. Nitrogen gas was previously introduced to jacket 33Jat a temperature of at least 50° F. with control valve 45 in connectionJ_(N2) to support the transition phase. Introducing path C vapor nearthe bottom of D-T vessel 33-1 and bubbling it through the sub-cooledliquid will provide more effective heating.

Draining of D-T vessel 33-1 is facilitated by reintroducing nitrogen gasat a pressure of at least 1250 psia and temperature of at least 50° F.through connection V_(N2) and valve 43, thereby increasing the pressureof D-T vessel 33-1 to at least 1200 psia and replacing the sub-cooledliquid with nitrogen as it drains. Then, drain control valve 37 isopened to direct D-T vessel 33-1 sub-cooled liquid to drain manifold 39and mixing manifold 41 for merging with the sub-cooled liquid from pathB. Drain control valve 37 is closed when D-T vessel 33-1 is drained ofsub-cooled liquid.

D-T vessel 33-1 is prepared for its next deposition batch by placingvalve 43 in connection V_(N2) into service along with valve 49 in ventconnection V₃₃ to control operating pressure and temperature usingnitrogen gas at a temperature of at least −150° F. Jacket 33J isprepared for the next batch by placing valve 45 in connection J_(N2)into service along with valve 48 in vent connection JV to control jackettemperature to at least −150° F. by returning warmer nitrogen to storagetank area 52.

D-T vessels 33-2 and 33-3 were previously prepared for the depositionphase, and as an example, D-T vessel 33-2 is selected to be placed intoservice next following the same procedures as outlined for vessel 33-1,followed by selection of D-T vessel 33-3 and then back to selection ofD-T vessel 33-1, thereby making a continuous process.

The recombined paths A, B, and C in mixing manifold 41 form theregenerated process refrigerate at a temperature of at least 5° F. abovethe freezing point temperature of water (32° F.). The processrefrigerate then flows through expansion valve 34 for pressure controland control of the saturation temperature of evaporator 30 to at least5° F. below the temperature of the entering temperature of the lowtemperature heat source 51, thereby completing path A, B, and C cycles.

Nitrogen gas is supplied to D-T vessels 33 and jacket 33J from storagetank area 52, which also receives vented nitrogen gas, wherein requiredconditions are maintained for the cycle. Jacket 33J is equipped withdrain JD for off-line maintenance purposes.

Turbine by-passes are depicted as BP-1 and BP-2 for use during startupand low load operation to ensure that D-T vessels 33 receive the correctpressure and temperature vapor to facilitate deposition.

FIG. 1-A illustrates an alternate process 1A to using compressor 31 heatof compression in path B to superheat and reheat path A vapor sinceother heat sources may be available in a conventional plant such asspent or extracted steam, extracted flue gas, or waste heat as shownwith Q_(SH) with Q_(RH). Excess heat Q_(RTN) remaining in these highertemperature heat sources is returned to their respective sources asapplicable. Separately fired fossil fuel heaters may be used as well forQ_(SH) and Q_(RH). Alternate process 1A eliminates path B circuit usedin process 1, including compressor 31, hydraulic coupling 52, motor M,liquid expander 32-3, generator G3, and mixing manifold 41, resulting ina more economical and efficient plant. All other details are the same asoutlined for process 1. The additional fuel input and resultingpollutants required to provide heating steam or extracted flue gas forpath A vapor superheating may be offset with less fuel heat inputresulting from improved overall plant efficiency. Using low temperaturesources 51, such as solar mirror focused heat and geothermal heat, totransfer heat to evaporator 30 would also have heating capabilities tosuperheat path A vapor.

An example power cycle is described below to demonstrate process 1producing electricity, referencing FIG. 2 (CO₂ Pressure-EnthalpyDiagram), and FIG. 3 (CO₂ Phase Diagram).

FIG. 2 represents process 1 in a P-H diagram. Marked point 1 at theinlet to expansion valve 34 depicts supply of recombined paths A, B, andC sub-cooled liquid process refrigerate at a pressure of 1200 psia andtemperature of 40° F. Expansion valve 34 reduces the pressure to 900psia as shown by the vertical heavy-weighted black line as it suppliesevaporator 30. A low temperature source 51 with an entering temperatureof 80° F. transfers its heat to the sub-cooled liquid enteringevaporator 30, transitioning it into a saturated vapor exiting at apressure of 900 psia and temperature of 75° F., as marked by theheavy-weighted solid black line arrow (1 to 2).

The saturated vapor leaving evaporator 30 is split into paths A, B, andC. Path A flows to indirect heater 30-1. Path B flows to the inlet ofcompressor 31, wherein it is compressed to a superheated supercriticalpressure vapor of 3550 psia/250° F. (2 to 3B) as marked by along-dotted, heavy-weighted black line arrow. Path B then splits intopaths B1 and B2 (3B to 4B) for heat transfer to path A as it passesthrough two stages of heat exchangers (30-1 and 30-2). Path A issuperheated to 240° F. in indirect heater 30-1 (2 to 3A) by path B1,followed by isentropic expansion to 280 psia/75° F. through turbine 32-1(3A to 4A). Path A exhausts turbine 32-1 and flows to second stageindirect exchanger 30-2, wherein it is reheated to 230° F. (4A to 5A) bypath B2, followed by isentropic expansion through turbine 32-2 beforeexhausting as a superheated vapor at 75 psia/80° F. (5A to 6A). Paths B1and B2 recombine into path B downstream of heat exchangers 30-1 and 30-2at pressure/temperature conditions of 3540 psia/80° F. and then flowsthrough turbo-expander 32-3 (4B to 4C) to exit as a sub-cooled liquid atpressure/temperature conditions of 1250 psia/50° F., producing powerwith shaft-connected generator G3.

The low pressure superheated vapor leaving turbine 32-2 at point 6A isthen directed to turbo-expander 32-4 for isentropic expansion to producework with generator G4 and to reduce its temperature to −80° F. at apressure of 25 psia (6A to 7A), shown by the heavy-weighted black linearrow. The cooled vapor is then directed to venturi nozzle 36, whereinnitrogen gas spray S_(N2) is introduced at the throat at obtain amixture discharge temperature of at least −125° F. (7A to 8A), shown bythe short, double-thin black line arrow. Venturi nozzle 36 directs themixture into D-T vessel 33-1, which is operating with nitrogen gas at atemperature of at least −150° F. and a pressure so that the partialpressure of the cooled vapor is at least 14.7 psia to facilitate path Adry ice deposition (8A to 9A), shown by the long, double-thin black linearrow.

After D-T vessel 33-1 receives its full measure of dry ice, this trainis taken from service by closing shut-off valve 35 and venting nitrogengas V_(N2) back to storage tank area 52 through valve 49 in connectionV₃₃. During the closing of shut-off valve 35, D-T vessel 33-2 is placedinto service to provide a continuous process. D-T vessel 33-1 is thenpressurized to 100 psia by a portion of path C vapor through connectionPC and valve 44 to prevent dry ice sublimation to vapor and tofacilitate transitioning of dry ice to sub-cooled liquid, as shown bythe heavy-weighted broken black arrows from point 9A to the large blackdot marked on the 100 psia line.

The sub-cooled liquid in D-T vessel 33-1 is then heated and pressurizedto 900 psia by the remaining portion of path C vapor through connectionPC and valve 44. During the deposition phase, jacket 33J receivesnitrogen at a temperature greater than 50° F. through connection J_(N2)and valve 45 while venting cooler nitrogen to storage tank area 52through valve 48 in connection JV. The pressure in D-T vessel 33-1 isthen elevated to 1200 psia with nitrogen gas at a pressure of 1250 psiaand a temperature of at least 50° F. through connection V_(N2) and valve43 from storage tank area 52. Drain control valve 37 is then opened todirect D-T vessel 33-1 sub-cooled liquid to drain manifold 39, and thento mixing manifold 41 to merge with path B sub-cooled liquid leavingturbine expander 32-3, forming a recombined process refrigerate.

The recombined process refrigerate in mixing manifold 41, now at atemperature of at least 40° F., is then returned to expansion valve 34as the process refrigerate, labeled as point 1, completing the cycles ofpaths A, B, and C. These functions are shown on FIG. 2 by theheavy-weighted solid black line arrow from the dot on the 100 psia lineto point 1. Expansion valve 34 controls the saturation temperature ofthe process refrigerate in evaporator 30 to 75° F. by isenthalpicreduction of the pressure of the process refrigerate to 900 psia asshown by the vertical heavy-weighted black line from point 1.

The examples shown in this disclosure to demonstrate process 1 may bemodified to suit design conditions of manufacturers, including choice ofrefrigerate, operating pressures and temperatures, design of turbinesfor other pressure and temperature conditions, or splitting of paths A,B, and C into other mass flow proportions.

In storage tank area 50, shown enclosed in heavy-weighted dotted-blacklines, CO₂ pressure and temperature conditions are maintained forprocess 1 so that sub-liquid may be supplied during startups or loadincreases, and sub-liquid may be received during load reductions orshutdowns. In storage tank area 52, shown in enclosed lightly-weighteddotted-black lines, nitrogen gas conditions are maintained bycontrolling pressure and temperature so that D-T vessels 33 may besupplied nitrogen when required and receive nitrogen when vented.

As may be noted on FIG. 2, compressor 31 enthalpy of compression (29BTU/lb) is considerably less than the total enthalpy of expansion (93BTU/lb) provided by turbines 32-1, 32-2, 32-3, and 32-4. Assuming a 50%split between paths A and B, the net positive power production is 69% ofgross output. The example below shows the estimated power producingcapabilities of this disclosed cycle.

Assumptions: Combine with Conventional 200 gross megawatt/hour PowerPlant

*Condenser Cooling Water as Low Temperature Source 51:

-   -   Water Mass Flow=51,382,500 lb/hr    -   Water Temperature In/Out of Evaporator30 =80° F./50° F.    -   Differential Enthalpy=30 BTU/lb    -   Heat Content Available=1,541.5×10⁶ BTU/hr

CO₂ Process Refrigerate in Evaporator:

-   -   Temperature/Enthalpy Entering Evaporator=40° F./40 BTU/lb    -   Saturation Pressure/Temperature=900 psig/75° F.    -   Vapor Saturation Enthalpy=125 BTU/lb    -   Differential Enthalpy=85 BTU/lb    -   Mass Flow to Evaporator=1,541.5×10⁶/85=18,135,000 lb/hr    -   Path A, B, and C Mass Flow=6,045,000 lb/hr each

Turbine and Compressor Isentropic Efficiencies, η_(j)=90%

Generator Efficiency, η_(g)=98%

Net Enthalpy Differential, ΔH_(N), BTU/lb=93−29=64 BTU/lb (FIG. 2)

Pump and Refrigeration Auxiliary Power Losses Not Considered

Heat Loss to the Environment=0

Net Work in Megawatts, MWn:

MWn=Mass Flow, lb/hr×ΔH _(N), BTU/lb×η_(g)×η_(j)/(3412×1000)

-   -   Where, 3412=BTU per kilowatt hour

MWn=6,045,000×64×0.98×0.90/(3412×1000)=100

In summary, approximately 100 MW_(N) is produced from the heat contentof the cooling water of a conventional 200 MW_(N) power plant, which iscurrently rejected into the atmosphere by a cooling tower or to a nearbycooling water source.

*Note: When heat content is extracted from power plant condenser coolingwater, special care should be exercised to detect and prevent CO₂contamination of the cooling water returning from evaporator 30 to thecondenser. CO₂ may cause corrosion problems and leaks in the condenserthat enter the boiler feedwater condensate, thereby decreasing the pH ofthe condensate and possibly causing corrosion problems in downstreamequipment. The best option to avoid this event is to install two fullcapacity evaporators 30 that operate in parallel with shared loads sothat the evaporator 30 leaking CO₂ can be taken off-line to isolate itfor repairs, while its load is smoothly transferred to the otherevaporator 30.

What is claimed is:
 1. A method of producing electric power, the methodcomprising the steps of: extracting a heat content from a lowtemperature heat source, the low temperature heat source comprising oneof water, steam, a gas, or a solid; indirectly transferring said heatcontent to a process refrigerate within an evaporator, the processrefrigerate comprised of carbon dioxide; and evaporating the processrefrigerate within the evaporator with said heat content, wherein theprocess refrigerate enters the evaporator as a sub-cooled liquid orsaturated mixture and exits the evaporator as a vapor; and facilitatingtransfer of said heat content to the process refrigerate by supplyingthe process refrigerate to the evaporator through an expansion valve,wherein pressure is controlled to maintain the process refrigeratesaturation temperature at least 5° F. less than the temperature of thelow temperature heat source; directing the process refrigerate vaporfrom the evaporator to a first path as a first path vapor, a second pathas a second pass vapor, and a third path as a third path vapor;superheating the first path vapor in at least one indirect heatexchanger; directing the superheated first path vapor to at least oneturbine for expansion and producing work; directing the expanded firstpath vapor into at least one gas turbo-expander for further expansionand producing work, thereby producing a cooler first path vapor;directing the cooler first path vapor into at least one venturi nozzle(convergent-divergent nozzle) for further expansion and further coolingto less than the dry ice deposition temperature of −109.3° F.; anddirecting a nitrogen gas spray at a temperature of less than −150° F.into the throat of the at least one venturi nozzle to merge with thesaid cooler first path vapor, thereby producing a mixture of at least25° F. less than the carbon dioxide dry ice deposition temperature; anddirecting the mixture from the at least one venturi nozzle into adeposition-transition vessel, wherein the deposition-vessel is operatingin a nitrogen gas atmosphere at a temperature of at least −150° F. andat a pressure so that the partial pressure of the said cooler first pathvapor is of least 14.7 psia and a temperature of at least −125° F.,thereby facilitating deposition of a first path dry ice; collecting afull measure of the first path dry ice in the deposition-transitionvessel and then venting said nitrogen gas atmosphere to a storage tank;and directing a portion of said third path vapor to thedeposition-transition vessel, thereby elevating the pressure of thedeposition-vessel above the triple point pressure and preventingsublimation of said first path dry ice to a vapor and to cause meltingof said first path dry ice to a sub-cooled liquid; and elevating thepressure of said deposition-transition vessel to at least 900 psia withthe remaining portion of said third path vapor, thereby completing thetransitioning of the first path dry ice to a first path sub-cooledliquid and heating the sub-cooled liquid to a higher temperature;elevating said second path vapor to a supercritical pressure andsuperheated temperature in at least one compressor, thereby forming asupercritical second path vapor; directing the supercritical second pathvapor to the at least one indirect heat exchanger, such that heat fromthe supercritical second path vapor is transferred to the first pathvapor and the supercritical second path vapor exits the at least oneheat exchanger as supercritical second path liquid; and directing saidsupercritical second path liquid to at least one liquid turbo-generatorto produce work, thereby producing a second pass sub-cooled liquid at apressure of at least 1250 psia; directing the second pass sub-cooledliquid to a mixing manifold; directing a volume of nitrogen gas at apressure of at least 1250 psia and temperature of at least 50° F. to thedeposition-transition vessel, thereby elevating the pressure of thedeposition-vessel to at least 1200 psia to facilitate draining of thesub-cooled liquid; directing said sub-cooled liquid contents in thedeposition-transition vessel to the mixing manifold, wherein saidsub-cooled liquid is merged with said second path sub-cooled liquid,thereby regenerating the process refrigerate at a temperature of atleast 5° F. above the freezing point temperature of water; and directingthe process refrigerate from the mixing manifold to at least oneexpansion valve, wherein pressure is controlled to maintain the processrefrigerate saturation temperature in the evaporator at least 5° F.below the temperature of the entering low temperature heat source;directing said process refrigerate from the at least one expansion valveto the evaporator, thereby completing the first, second, and third pathcycles.
 2. The method according to claim 1, wherein said low temperatureheat source comprises one of a cooling water or cooling air of a powerplant condenser, a concentrated solar heat from a mirror farm, ageothermal source, a solar heated pond, and a solar storage heat source.3. The method according to claim 1, further comprising implementing themethod with an alternate process; wherein an alternate heat source isused to superheat the first path vapor, thereby, eliminating the secondpath.
 4. The method according to claims 1, 2, and 3, further comprisingimplementing the method, wherein the alternate heat source to superheatthe first path vapor comprises one of a concentrated solar heat from amirror farm, a geothermal source, an exhaust gas from a boiler, gasturbine, or separately fired heater, flue gas or steam extracted from apower plant boiler, and spent or auxiliary steam extracted from a powerplant cycle.
 5. The method according to claim 1, wherein said processrefrigerate is carbon dioxide or any refrigerate with similarproperties.
 6. The method according to claim 1, wherein thedeposition-transition vessel comprises a plurality ofdeposition-transition vessels arranged in parallel paths and operatedsequentially to provide a continuous first path cycling process bytiming of the parallel paths in alternation.
 7. The method according toclaim 1, the method further comprising: splitting the second path at anoutlet of the at least one compressor, wherein a portion of thesupercritical second path vapor is supplied to each of the plurality ofheat exchangers, such that heat from the supercritical second path vaporis transferred to the first path and the supercritical second path vaporexits each of the plurality of heat exchangers as supercritical secondpath liquid; and recombining the supercritical second path liquid fromsaid plurality of heat exchangers before entering the at least oneturbo-expander.
 8. The method according to claims 1 and 6, wherein theplurality of deposition-transition vessels are each enclosed with ajacket, wherein a nitrogen gas atmosphere is maintained at a temperatureof less than −150° F. to insulate against heat loss during the firstpath vapor deposition phase to dry ice and a nitrogen gas atmosphere ismaintained at a temperature of at least 50° F. to insulate against heatloss during the first path dry ice transition phase to sub-cooledliquid.
 9. The method according to claims 1 and 8, wherein nitrogen gaspressure and temperature conditions in the deposition-transition vesseland jacket are maintained by one or more of a vacuum pump, an ejectordevice, and a compressor.
 10. The method according to claims 1 and 3,further comprising implementing the method as a retrofit in combinationwith an existing power plant, in combination with a new power plant, oras a stand-alone power plant.
 11. The method according to claims 1 and3, further comprising implementing the method as a retrofit incombination with an existing plant or in combination with a new plant,wherein a cooling water tower is not required when the condenser coolingwater is recirculated from the carbon dioxide evaporator back to thecondenser.
 12. The method according to claims 1 and 3, furthercomprising implementing the method as a retrofit in combination with anexisting plant or in combination with a new plant, wherein a continuousflow of cooling water to the condenser from a nearby water source and acontinuous return from the condenser to the nearby water source is notrequired when the condenser cooling water is recirculated from thecarbon dioxide evaporator back to the condenser.